The present invention relates to a toothbrush wherein the bristle hardness may be varied by adjusting the operative bristle length.
There has existed for a long time a need for toothbrushes whose bristle hardness may be adjusted by the user. This is desirable in order to be able to impart the suitable and required intensity to the cleaning procedure in accordance with the condition of the teeth and of the gums. The hardness and thus the cleaning power of the bristles is known to be directly correlated to their length. Thus the degree of hardness may be controlled directly by adjustment of the length of the bristles.
Brushes whose bristle length may be varied are known in the art. German Offenlegungsschrift No. 2,107,900 discloses a hardness-adjustable brush, comprising a brush plate, a perforated plate, and a cover. The perforated plate is adjustably arranged opposite the brush plate by means of a threaded pin and a nut thread interacting therewith and the adjustment takes place by means of a control knob or the like arranged above the bristle plate, the control knob being shaped like a drive gear and covered by a cover arranged on the bristle plate.
By means of this device, a hardness adjustment of the brushes may actually be achieved by an up and down movement of the perforated plate. This known device, which in principle should be applicable to toothbrushes, is apparently designed preponderantly for clothes and body scrubbing brushes. This device is a complicated assembly which necessitates a correspondingly expensive finishing. Another drawback of this device which is aggravating for toothbrushes is that the adjustment of the bristle length and thus of the brush hardness cannot be undertaken during the cleaning procedure. Rather, it requires an interruption of the cleaning and a separate regulating by means of the drive gear. Because of the size necessitated by the expensive configuration of the known, hardness-adjustable brush, an application to toothbrushes seems hardly possible.
In toothbrushes, however, it is absolutely necessary that construction be of the utmost simplicity and that adjustment of the bristle length may be achieved during the cleaning procedure.